1. Field of the Invention
The present invention relates generally to a color picture tube, and more particularly to an improvement of a phosphor screen of the color picture tube.
2. Description of the Related Art
A color picture tube generally comprises a faceplate having an inner surface provided with a phosphor screen; a vacuum envelope made of glass including a funnel connected integrally with the faceplate; and an electron gun for emitting electron beams, which is housed in a neck of the funnel.
As is shown in FIG. 1, a phosphor screen 7 comprises black light-absorption layers 14 made mainly of carbon, and phosphor layers 13B, 13G and 13R capable of emitting blue, green and red light. The light-absorption layers 14 are formed on a faceplate 2 in stripes or in a matrix. The phosphor layers 13B, 13G and 13R are formed over the light-absorption layers 14, similarly in stripes or in dots arranged in a matrix.
As has been stated above, in a widely used color picture tube, the three color phosphor layers 13B, 13G and 13R are formed in stripes or in dots, and the black light-absorption layers 14 are formed between the stripes of these phosphor layers 13B, 13G and 13R ("black stripe type color picture tube") or formed between the dots of the phosphor layers 13B, 13G and 13R ("black matrix type color picture tube"). The black light-absorption layers 14 are employed to enhance the contrast of images. Specifically, the layers 14 prevent light reflection, and absorb light in the vicinity of phosphor layers 13B, 13G and 13R where mislanding of electron beams is likely to occur.
In the black stripe type or black matrix type color picture tube, the contrast of images is enhanced by the light-absorption layers, but the improvement of luminance of images is limited. Published Unexamined Japanese Patent Application No. 52-74274 discloses a technique of improving the luminance, wherein the black light-absorption layers 14 with a light transmittance of 5 to 40% (i.e. "semitransparent") are employed thereby remarkably increasing the luminance.
The black light-absorption layers, however, function also as so-called guard band portions for absorbing mislanded electron beams. Thus, if the light-absorption layers are simply made semitransparent, the color purity and landing characteristics are deteriorated. Thus, this technique is disadvantageous in practical use.